The inductive role of testosterone in organizing sex differences in emotional behavior will be investigated. A developmental approach, which has already been adopted with some success, will describe the normal ontogeny of sex differences in open-field activity and cardiac regulation. The effect of neonatal TP in females will then be evaluated in a similar manner to discover how closely such a hormonal effect mimics the normal ontogeny of the male. The basic phenomenon will be further elucidated by studying the effect of castration of male rats shortly after birth in an effort to produce feminine behavorial development. Other experiments will evaluate whether the hormonal effects are (a) testosterone-specific, (b) dependent on the age of neonatal hormone treatment or (c) correlate with other behavioral consequences of hormone treatment. The role of ovarian, adrenal and thyroid secretions will be investigated as possible mechanisms mediating the neonatal hormonal effects on behavior.